Mysteries of the Monarch Butterfly

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February 22, 1999 -- Every winter, tens of millions of monarch butterflies migrate to the Oyamel (Balsa) forests west of Mexico City. This phenomenon has been closely studied by many scientists for decades, but remains unexplained. Join NPR's John Burnett as he sets out on a Radio Expedition with the foremost researcher of monarchs, biologist Lincoln Brower. They hike to 10,000 feet and -- surrounded by the millions of butterflies -- set up an experiment to learn more about the monarch's winter environment and witness this amazing event.

For more information, check out Journey North, a free Internet-based science education program that engages students in a global study of wildlife migration. The monarch migration is one of a dozen migrations tracked each year.